It is now common practice to coat workpieces by electrostatically depositing a layer of particulate resinous material upon them, thereafter integrating the particles using thermal fusion or other appropriate means. As shown for example in U.S. Pat. No. 3,865,610, issued Feb. 11, 1975, U.S. Pat. No. 3,889,015, issued Jun. 10, 1975, U.S. Pat. No. 3,901,185, issued Aug. 26, 1975, and U.S. Pat. No. 3,921,574, issued Nov. 25, 1975 (all of common assignment herewith), this technique has been utilized for insulating the slots and end surfaces of electric motor armature cores, and it is now widely used for that purpose on an industrial scale.
Armature cores are conventionally manufactured in the form of stacked lamina, punched or otherwise formed from metal plate. Lubricating substances are of course utilized in such metal cutting and forming operations, and as a practical matter some residual lubricant is almost invariably retained on the surfaces of the metal element, despite efforts made to remove it. The presence of such substances will interfere with the production of satisfactory insulating layers, and therefore a degreasing step is normally employed preliminarily to powder coating of the component, carried out in-line with the subsequent deposition and fusion steps.
As presently practiced however, degreasing does not effectively remove matter trapped between the lamina. As a result, residual lubricants and the like will volatilize during the heating that is carried out to effect fusion of the powder deposit, with the consequential off-gassing tending to produce pores and other electrical and physical defects and discontinuities.
It is of course common practice to use steam for removing grease and dirt from machinery, such as vehicle engines and the like. Also, Kawamura et al U.S. Pat. No. 4,391,016 discloses apparatus for degreasing elongated members, such as rod stock, which includes degreasing and predrying chambers; in the latter, steam is utilized to effect predrying.
Chlorinated and fluorinated hydrocarbon solvents, such as trichloroethylene and Freon products, are widely employed for metal degreasing, but such solvents are of course ecologically and environmentally undesirable; their use is therefore subject to serious constraints, imposed to maintain safe and pleasant working conditions and to ensure proper disposal. Because of their particularly noxious character, the vapors of such substances must not be permitted to escape into the atmosphere, and consequently they are normally used at relatively low temperatures, to avoid excessively active fuming, and are contained in tanks fitted with condensing coils for confining the vapors. As a result a relatively complex conveyor system must be employed to permit introduction of the workpieces at a level above the condensing coils, and passage therebelow for degreasing.